The present invention relates to an image forming apparatus such as a copier, printer, facsimile device, or the like, to which an electrophotographic method is applied, and its control method, and particularly, to a digital type image forming apparatus which forms an image by automatically detecting a size of the document and automatically selecting a transfer material corresponding to the size of the document, and its control method.
Recently, a digital type image forming apparatus which reads a document image and forms an image based on the read image data, is used. In this type image forming apparatus, the document image is read by a CCD image sensor, or the like, and the read-out image data is stored once in a memory. Image data stored in the memory is outputted after image processing such as reduction, enlargement, and rotation of the image is conducted corresponding to requests of the user, a latent image is formed on a photoreceptor, next, developed by developer and a toner image is formed, the toner image is transferred onto a predetermined transfer material, and the image is formed.
Further, at the start of image forming operations, a memory area appropriate for the document size is previously set, and after that, the image forming operations including image reading, sheet feeding of the transfer material, or similar operations, are started.
In contrast to that, in order to increase the productivity in the image formation, it is effective that transfer material having the size appropriate for the document size is selected from the document size information during image reading, sheet feeding of the transfer material is previously started, and it is on standby at the position of registration rollers in a sheet feed section. Accordingly, in order to increase the productivity in the digital type image forming apparatus, it is the presupposition that the document size or transfer material size is previously detected or set. However, the size of the transfer material can also be automatically selected from the document size information, and therefore, the detection of the document size is an important factor.
On the other hand, in the image forming apparatus, an automatic document feeding apparatus is provided to eliminate troublesomeness in which the operator sets the document on a platen for each sheet, thereby, the operator can easily copy a plurality of documents by only setting them on a placement tray. Further, document modes corresponding to each type of document are provided, for example, the same series document mode in which image formation is conducted by using only the same sized and regular sized document, and the different series mixture document mode in which irregular sized documents or different sized documents are mixed, and image formation is conducted by using them, are applied.
In the image forming apparatus provided with such an automatic document feeding apparatus, the document size is automatically detected and the corresponding transfer material is automatically selected, and the image formation is conducted.
As for the above-described document size detection method, many methods are commonly known, and as the first method, there is a method which is widely used in the conventional analog type copier, and in which the document is conveyed onto a platen on which the document is placed and the image is exposed, and the document size is detected by using an exposure light source on the platen. In this first method, because the document size is detected after the document is conveyed from the automatic document feeding apparatus onto the platen, the time period for conveying the document onto the platen is necessary, and so much time period is passed to start the image formation, thereby, the copy productivity is lowered, which is a problem.
The second method is a method in which the lateral width of the document is detected by the position of the lateral width regulation plate on the document placement tray, and the document is fed and the leading edge and trailing edge are detected, thereby, the length (longitude) in the conveyance direction is detected, and thereby, the document size is detected. In this second method, because a sensor to detect the document size is provided on the conveyance path, the document size can not be detected if the detection is not conducted after the document is fed and the overall length (longitude) of the document is sent. Therefore, this method is slightly improved as compared to the first method, however, it is not an essential improvement, and in the same manner as in the first method, the document conveyance time is necessary, and the time period necessary to the start of the image formation is long, thereby, the copy productivity is lowered, which is a problem.
As the third method to solve the first and second problems, the present inventors have proposed a method previously in which the longitudinal and lateral document sizes are detected on the document placement tray, thereby, the image formation can be immediately started, a nd copy can be conducted with high productivity, and have intended to solve the defects of the first and second method, and to increase the copy productivity.
However, in further consideration from the view point of reliability by the present inventors, it has been found that the document size detection has a new problem. That is, when the operator places the a plurality of document sheets on the document placement tray, it is not necessarily follow that overall document sheets are accurately aligned and correctly placed. Accordingly, when the document sheets are irregularly placed, the irregular document sheet is detected by a sensor which detects the larger document sheet, and the length of longitudinal or lateral side is detected to be larger than the size of the original one, thereby, the document sheet can not be detected as the regular size. For example, in the document size detection, when the document size is detected by arranging the document detection sensors corresponding to each regular size, when A4R sized document is placed, even if the lateral width can be detected to be the regular width of the A4R sized sheet, if the longitudinal length is detected to be the length of the B4 sized sheet which is longer than that of the A4R sized sheet, this document sheet size is detected to be A4R sized width and B4 sized length, and can not be detected as a predetermined A4R regular sized sheet.
In this case, when the same series document mode is set, the transfer material of the corresponding size can not be selected from the regular sized transfer material, resulting in stoppage of image forming operations. Further, in the same manner as described above, also when the same series document mode is set to irregular sized documents, the image forming operation can not be started, resulting in stoppage of image forming operations.
On the other hand, in the productivity of the image formation, when the size of document sheets are the same, if the first document size information is obtained, the second and subsequent document sizes are not detected and regarded as the same size, and the document size detection process and the automatic transfer material selection process are neglected, and the sheet feeding operation can be started earlier, thereby, the image formation productivity can be increased. However, when the different series document mode which is applied for different type document sizes, is conducted, it is necessary that the image formation is carried out by detecting the document size for each document sheet even if the document sheets are the same size, and transfer sheet feeding can not be carried out earlier, thereby, such a problem occurs that the image formation productivity is lowered.